How does your character smell? Do they wear perfume or cologne?
Have you ever smelled ammonia? Or cleaned a fish tank or a cat litter?
Well, it’s also used in cleaning. Given the acid rain that falls on Cybertron (an thus the air would have a bit of an acidic pH), ammonia is a common on world material used in the wash racks as well as a preventative against corrosion.
It’s not an overpowering smell (like when you clean the fish tank), but its definitely there, and though while we might find it repulsive (one, Shockwave has no olfactory sensors) that doesn’t mean those on Cybertron would.
He also smells like bleach and other cleaning materials.
He smells like his lab.
(So sometimes he smells like burnt metal depending on what he was working on, but he rarely smells strongly of one specific thing, unless it gets messy (like working with a spark eater).)